Misfirings from my Neurons

In my games other planes are basically other planets elsewhere in the universe. So the Astral Plane is real space. It can be traverse via Technology (warp drives and what not) or Magic (Planar Gates). However given that Ethereal space (the source of magic) is lumpy and not all worlds have high Magic levels (or High Axioms per Torg), not all plane(t)s can be reached by Magic. Similarly high magic can separate some worlds from Technological approach.

Two examples:
1) Arda: the home game world is surrounded by a huge sphere of magicks called the Maelstrom which contains the Elemental Planes accessible from Arda (which lies within the sphere).
2) The Abyss: A huge (Integral Trees-style) open ring of atmosphere, magick and rocks surrounding a sun. Starships fail when coming anywhere near it.

Magical planets tend to be labeled Navigation hazards. Similarly Technological planets are unknown to magical worlds. There may be a few worlds that connect the two and those are rare and interesting places (say like a Cynosure or similar multi-versal spot).

My game universe posits only the one universe as being friendly. Anything from another universe (say via the Bleed or your game equivalent) is terrifying and completely alien.